198 research outputs found
Heralded generation of entangled photon pairs
Entangled photons are a crucial resource for quantum communication and linear
optical quantum computation. Unfortunately, the applicability of many
photon-based schemes is limited due to the stochastic character of the photon
sources. Therefore, a worldwide effort has focused in overcoming the limitation
of probabilistic emission by generating two-photon entangled states conditioned
on the detection of auxiliary photons. Here we present the first heralded
generation of photon states that are maximally entangled in polarization with
linear optics and standard photon detection from spontaneous parametric
down-conversion. We utilize the down-conversion state corresponding to the
generation of three photon pairs, where the coincident detection of four
auxiliary photons unambiguously heralds the successful preparation of the
entangled state. This controlled generation of entangled photon states is a
significant step towards the applicability of a linear optics quantum network,
in particular for entanglement swapping, quantum teleportation, quantum
cryptography and scalable approaches towards photonics-based quantum computing
SAS multipass interferometry for monitoring seabed deformation using a high-frequency imaging sonar
Abstract-. This paper presents the results of a two years project led and funded by Eni from 2008 to 2010 with the aim of supporting
the development and experimentation of innovative technology for environmental monitoring. The problem addressed is the precise estimate of possible altimetric variations of the seabed through long-term monitoring. The selected methodology consists in the application of repeat-track interferometry to high-resolution, high-frequency sonar data collected from an AUV during repeated surveys of a seafloor area of interest. The paper describes the experimental measurements conducted at sea, the SAS and interferometry methodologies developed, and the results obtained on artificial objects sitting on the seabed. The quality of the achieved focusing is analyzed. The achieved repeat-pass SAS interferograms are shown and analyzed. The coherence along time of the particular
kind of seabed (silty sand) characterizing the experimental area is presented and the utility of artificial reflectors for long-term SAS interferometry is discussed.Published673-6832.5. Laboratorio per lo sviluppo di sistemi di rilevamento sottomariniN/A or not JCRreserve
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment
GEMS (Gamma Energy Marine Spectrometer) is a prototype of an autonomous radioactivity sensor for underwater measurements, developed in the framework for a development of a submarine telescope for neutrino detection (KM3NeT Design Study Project). The spectrometer is highly sensitive to gamma rays produced by 40K decays but it can detect other natural (e.g., 238U,232Th) and anthropogenic radio-nuclides (e.g., 137Cs). GEMS was firstly tested and calibrated in the laboratory using known sources and it was successfully deployed for a long-term (6 months) monitoring at a depth of 3200 m in the Ionian Sea (Capo Passero, offshore Eastern Sicily). The instrument recorded data for the whole deployment period within the expected specifications. This monitoring provided, for the first time, a continuous time-series of radioactivity in deep-sea.In press4.5. Studi sul degassamento naturale e sui gas petroliferiJCR Journalope
GEMS: Underwater spectrometer for long-term radioactivity measurements
GEMS (Gamma Energy Marine Spectrometer) is a prototype of an autonomous radioactivity sensor for underwater measurements, developed in the framework for a development of a submarine telescope for neutrino detection (KM3NeT Design Study Project). The spectrometer is highly sensitive to gamma rays produced by 40K decays but it can detect other natural (e.g., 238U,232Th) and anthropogenic radio-nuclides (e.g., 137Cs). GEMS was firstly tested and calibrated in the laboratory using known sources and it was successfully deployed for a long-term (6 months) monitoring at a depth of 3200 m in the Ionian Sea (Capo Passero, offshore Eastern Sicily). The instrument recorded data for the whole deployment period within the expected specifications. This monitoring provided, for the first time, a continuous time-series of radioactivity in deep-sea
Monitoring of a methane-seeping pockmark by cabled benthic observatory (Patras Gulf, Greece)
A new seafloor observatory, the gas monitoring
module (GMM), has been developed for continuous and
long-term measurements of methane and hydrogen sulphide
concentrations in seawater, integrated with temperature (T),
pressure (P) and conductivity data at the seafloor. GMM
was deployed in April 2004 within an active gas-bearing
pockmark in the Gulf of Patras (Greece), at a water depth of
42 m. Through a submarine cable linked to an onshore
station, it was possible to remotely check, via direct phone
connection, GMM functioning and to receive data in nearreal
time. Recordings were carried out in two consecutive
campaigns over the periods April–July 2004, and September
2004–January 2005, amounting to a combined dataset
of ca. 6.5 months. This represents the first long-term
monitoring ever done on gas leakage from pockmarks by
means of CH4+H2S+T+P sensors. The results show
frequent T and P drops associated with gas peaks, more
than 60 events in 6.5 months, likely due to intermittent,
pulsation-like seepage. Decreases in temperature in the
order of 0.1–1°C (up to 1.7°C) below an ambient T of ca.
17°C (annual average) were associated with short-lived
pulses (10–60 min) of increased CH4+H2S concentrations.
This seepage “pulsation” can either be an active process
driven by pressure build-up in the pockmark sediments, or a
passive fluid release due to hydrostatic pressure drops
induced by bottom currents cascading into the pockmark
depression. Redundancy and comparison of data from
different sensors were fundamental to interpret subtle proxy
signals of temperature and pressure which would not be
understood using only one sensor.Published297-302JCR Journalreserve
NEMO-SN1 (Western Ionian Sea, off Eastern Sicily): A Cabled Abyssal Observatory with Tsunami Early Warning Capability
The NEMO-SN1 (NEutrino Mediterranean Observatory - Submarine
Network 1) seafloor observatory is located in the central
Mediterranean, Western Ionian Sea, off Eastern Sicily Island (Southern
Italy) at 2100 m water depth, 25 km from the harbour of the city of
Catania. It is a prototype of cabled deep-sea multiparameter
observatory, and the first operating with real-time data transmission in
Europe since 2005. NEMO-SN1 is also the first-established node of
EMSO (European Multidisciplinary Seafloor Observatory,
http://emso-eu.org), one of the European large-scale research
infrastructures. EMSO will address long-term monitoring of
environmental processes related to marine ecosystems, climate change
and geo-hazards. NEMO-SN1 will perform geophysical and
environmental long-term monitoring by acquiring seismological,
geomagnetic, gravimetric, accelerometric, physico-oceanographic,
hydro-acoustic, bio-acoustic measurements to study earthquake and
tsunami generation, and to characterize ambient noise which includes
marine mammal sounds, and environmental and anthropogenic sources.
NEMO-SN1 is also equipped with a prototype tsunami detector, based
on the simultaneous measurement of the seismic and bottom pressure
signals and a new high performance tsunami detection algorithm.
NEMO-SN1 will be a permanent tsunami early warning node in
Western Ionian Sea, an area where very destructive earthquakes have
occurred in the past, some of them tsunamigenic (e.g., 1693, M=7.5;
1908, M=7.4).
Another important feature of NEMO-SN1 is the installation of a low
frequency-high sensibility hydrophone and two (scalar and vector,
respectively) magnetometers. The objective is to improve the tsunami
detection capability of SN1 through the recognition of tsunami-induced
hydro-acoustic and electro-magnetic precursors.SubmittedRhodes, Greece3A. Ambiente Marinorestricte
An innovative tsunami detector operating in tsunami generation environment
On August 25th 2007 a tsunami detector installed onboard the multi-parameter observatory GEOSTAR was successfully deployed at 3200 b. s. l. in the Gulf of Cadiz, Portugal. This activity is within the NEAREST EC Project (http://nearest.bo.ismar.cnr.it/ ). Among other deliverables, the NEAREST project will produce and test the basic parts of an operational prototype of a near field tsunami warning system. This system includes an onshore warning centre, based on the geophysical monitoring networks which are already operating, and a tsunami detector deployed on board GEOSTAR at the sea bottom. On land the warning centre is in charge of collecting, integrating, and evaluating data recorded at sea. At the sea bottom data is recorded and processed by an advanced type of tsunami detector which includes: a pressure sensor, a seismometer and two accelerometers. The detector communicates acoustically with a surface buoy in two-way mode. The buoy is equipped with meteo station, GPS and tiltmeter and is connected to a shore station via satellite link. The prototype is designed to operate in tsunami generation areas for detection-warning purpose as well as for scientific measurements. The tsunami detector sends a near real time automatic alert message when a seismic or pressure threshold are exceeded. Pressure signals are processed by the tsunami detection algorithm and the water pressure perturbation caused by the seafloor motion is taken into account. The algorithm is designed to detect small tsunami waves, less than one centimetre, in a very noisy environment. Our objective is to combine a novel approach to the tsunami warning problem, with a study of the coupling between the water column perturbations and sea floor motion, together with the long term monitoring of geophysical, geochemical and oceanographic parameters
Tsunami Warning prototype in the frame of the EC NEAREST project.
Nell' ambito del progetto NEAREST finanziato dalla EC sono stati
sviluppati alcuni elementi di un sistema di allerta per tsunami, fra i quali un
prototipo di detector di onde anomale istallato a bordo dell' osservatorio
abissale GEOSTAR: l' osservatorio con il detector di onde anomale ha operato
per un anno nel Golfo di Cadice, a 3200m di profonditĂ PublishedSassari1.8. Osservazioni di geofisica ambientaleope
De Broglie Wavelength of a Nonlocal Four-Photon
Superposition is one of the most distinct features of quantum theory and has
been demonstrated in numerous realizations of Young's classical double-slit
interference experiment and its analogues. However, quantum entanglement - a
significant coherent superposition in multiparticle systems - yields phenomena
that are much richer and more interesting than anything that can be seen in a
one-particle system. Among them, one important type of multi-particle
experiments uses path-entangled number-states, which exhibit pure higher-order
interference and allow novel applications in metrology and imaging such as
quantum interferometry and spectroscopy with phase sensitivity at the
Heisenberg limit or quantum lithography beyond the classical diffraction limit.
Up to now, in optical implementations of such schemes lower-order interference
effects would always decrease the overall performance at higher particle
numbers. They have thus been limited to two photons. We overcome this
limitation and demonstrate a linear-optics-based four-photon interferometer.
Observation of a four-particle mode-entangled state is confirmed by
interference fringes with a periodicity of one quarter of the single-photon
wavelength. This scheme can readily be extended to arbitrary photon numbers and
thus represents an important step towards realizable applications with
entanglement-enhanced performance.Comment: 19 pages, 4 figures, submitted on November 18, 200
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